Automatic Belt Tracking System

ABSTRACT

In an aspect of the present invention, a system and method are provided that detect belt mis-tracking and in response, automatically adjusts. In some implementations, the system and method are implemented in conjunction with a weigh feeder or weigh belt. In other implementations, the system and method are implemented in conjunction with other devices that convey material via one or more belts. The system and method can be implemented by providing one or more sensors that detect belt mis-tracking, a motor for adjusting a belt pulley and one or more controllers that operate the motor in response to signals from the one or more sensors.

TECHNICAL FIELD

This disclosure relates to an automatic belt tracking system.

BACKGROUND

The precise metering of materials (e.g., dry solids) is important inmany applications, including numerous manufacturing processes in variousindustries. Usually when material is continuously metered into aprocess, it must be precisely controlled at a specific feed rate so thatthe process functions as designed, the product formulation is correct,and the quality of the end product of the process does not suffer. Inother applications, it is important to just keep track of the amount ofmaterial that has passed through a process, and controlling the feedrate is less important, or not important at all. Many of theseapplications are automated, and productivity concerns demand that theyproceed without human intervention to the greatest extent possible.

Various kinds of weigh feeders have been used for weighing and feedingmaterials such as sand, gravel, grain, foodstuffs, chemicals,pharmaceuticals, ceramics, etc. In general, material is provided to aweigh feeder continuously or periodically and the weigh feederdischarges the material at a desired output rate. Different weighfeeders, however, have different capabilities, which depend on thedesign of the weigh feeder and its principle of operation. Weight-lossand weigh belt feeders are two types of commonly used weigh feeders.

Weigh belt feeders can weigh material as the material is transported bya moving belt and usually receive a continuous supply of material,generally from an overhead storage supply. In one configuration (e.g.,the Acrison, Inc., 260 Belt Weigher/Feeder), material travels from astorage supply, down a chute and onto a rear portion of the belt, whichis not weighed. As the belt moves, the material on the belt passes overa weighing section, and a weight signal is produced that corresponds tothe weight of material traveling across the weighing section. The weightsignal is processed in conjunction with another signal, representing thespeed of the belt, by the weigh feeder's controller to derive a feedrate signal. The feed rate signal is compared to the feed rate selectedby the user, and the weigh feeder's controller continuously adjusts avariable speed drive powering the belt to maintain the desired feedrate.

A weigh belt feeder may also utilize a feeding mechanism to activelyfeed material onto the belt (e.g., a screw conveyor/feeder, anotherbelt, a vibratory tray device, etc.). Although such active feeding (orprefeeding) is different from the method of gravimetric feedingdescribed above, the material on the belt is weighed in a similarmanner. Such active feeding of material onto the weigh belt can providea greater degree of physical control over the material being fed. Inthis mode of operation, the weigh belt moves at a fixed constant speed,and the feed rate of the feeding mechanism is variable. Thus, the weighfeeder's controller continuously modulates the output of the feedingmechanism that feeds material onto the belt to maintain a selected feedrate of material discharging off the belt. Material is usually providedto the feeding mechanism directly from a storage supply, for example, ahopper or silo.

A different type of weigh belt feeder (e.g., the Acrison, Inc., 203/210weigh belt feeders) operates by weighing the entire weigh belt assembly,while a pre-feeder (e.g., a screw conveyor and/or feeder, another belt,or a vibratory type device) meters material onto the weigh belt, whichoperates at a fixed constant speed. The output of the pre-feeder, whichis equipped with a variable speed drive, is continuously modulated bythe weigh feeder's controller so that the rate at which material passesacross the weigh belt accurately matches the selected feed rate. In sucha weigh feeder, material is also usually supplied to the pre-feederdirectly from a storage supply.

A weight-loss feeder (e.g., the Acrison, Inc. 400 Series weight-lossfeeders) comprises a material supply hopper and a feeding mechanismmounted on a scale. As material is fed out of the scale-mountedmetering/supply system, a decreasing weight signal is produced, which isprocessed by the weigh feeder's controller in conjunction with a timesignal to calculate a feed rate. The feeding mechanism of a weight-lossweigh feeder is equipped with a variable speed drive so that its feedrate output can be continuously modulated by the weigh feeder'scontroller in order to maintain the selected feed rate. The supplyhopper of a weight-loss weigh feeder can be periodically refilled.

In other processes, it is desirable to know how much material has beenfed, and control of the amount is not necessary. These applications canutilize a weigh belt weigher, which only weighs the amount of materialbeing conveyed by the belt over a given amount of time. Like the twotypes of weigh belt feeders discussed above, weigh belt weighers conveymaterial via a moving belt. Indeed, many devices employed in industryconvey material via a moving belt.

SUMMARY

In an aspect of the present invention, a system and method are providedthat detect belt mis-tracking and in response, automatically adjusts. Insome implementations, the system and method are implemented inconjunction with a weigh feeder or weigh belt. In other implementations,the system and method are implemented in conjunction with other devicesthat convey material via one or more belts. The system and method can beimplemented by, e.g., providing one or more sensors that detect beltmis-tracking, a motor for adjusting a belt pulley and one or morecontrollers that operate the motor in response to signals from the oneor more sensors.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Various features andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts an overview of an implementation of a weigh beltweigher/feeder system.

FIG. 2 is a diagram of an implementation of a weigh belt weigher/feeder.

FIG. 3A is a diagram of an implementation of a mis-tracking adjustmentmechanism.

FIG. 3B is an alternate view of a weigh belt weigher/feeder system.

FIG. 4A illustrates a first example of belt mis-tracking, and animplementation of sensors.

FIG. 4B illustrates a second example of belt mis-tracking, and animplementation of sensors.

FIG. 5 is a schematic of an implementation of an automatic beltmis-tracking adjustment system.

FIG. 6 is a flow chart illustrating an implementation of a method forautomatic belt mis-tracking adjustment.

The figures are not drawn to scale.

DETAILED DESCRIPTION

The following is a description of preferred implementations, as well assome alternative implementations, of a system and method for automaticbelt mis-tracking adjustment and/or correction.

In many spheres of industry, belt conveyors are widely utilized totransport all sorts of material from one location to another. In thevarious processing industries, belt conveyors are commonly used totransport, e.g., dry bulk solid ingredients from one point to another.Belt conveyors are also used as the conveying/weighing apparatus forweigh belts (e.g., as a weigh belt feeder or as a weigh belt weigher).In such applications, the weight of the material on the belt is weighedas the belt passes over a weight sensing section.

Belt conveyor mechanisms can be subject to belt mis-trackingdifficulties, typically caused by belt expansion or contraction, dirt ordust accumulation/adhesion on the underside of the belt or on the beltpullies (upon which the belt rides), uneven belt loading, as well asother mechanical reasons. When this occurs, and if not addressed in timeso that the belt mis-tracking can be corrected (which is commonly amechanical adjustment, often made to the belt's rear pulley), weighingperformance can be adversely affected and/or the belt can be irreparablydamaged. Unfortunately, in most continuous processing/manufacturingoperations where belt conveyors are utilized, and more specifically,where weigh belt feeders or weighers are concerned, a mis-tracking belt(or one that is damaged as a result of mis-tracking) requires that theprocess be shut down to either correct the mis-tracking belt, and/or toreplace a damaged belt.

FIG. 1 depicts an overview of an implementation of a weigh beltweigher/feeder system 100 incorporating automatic belt mis-trackingadjustment. The weigh belt weigher/feeder system 100 incorporatesseveral major components in this implementation. Chassis 101, amongother things, provides structural support for the mechanical aspects ofthe system 100, and maintains those aspects in substantially operationalalignment. Chassis 101 is normally constructed of metal, e.g., steel,but can vary to suit the application. Product storage supply 102supplies material for weighing/conveyance to the belt 114, and can takethe form of, e.g., a hopper or screw conveyor. Material from the productstorage supply 102 travels onto belt 114 which is coupled to frontpulley 115 and rear pulley 116. The belt 114, as shown in thisimplementation, is the endless type and has portions which, during agiven instant of belt travel, are parallel to each other. The portionsthat are parallel to each other may be differentiated from each other byreferring to the “top half” and “bottom half” of the belt. Theseportions are substantially linear (as opposed to some portions of thebelt 114 which are wrapped around pulleys 115 and 116). The belt 114 hasedges which define its width.

In the implementation, pulleys 115 and 116 rotate in a counter-clockwisedirection, thereby transporting material from the material storagesupply 102 toward output opening 107. In this implementation, only thefront pulley 115 is driven (here, by gearmotor drive 103), whereas therear pulley 116 is not powered. The speed of the belt is detected by aspeed sensor 104 coupled to the rear pulley 116. The sensor 104 can takemany forms, such as a tachometer based on, e.g., a magnet that induces achanging magnetic field upon a Hall Effect transistor or a stroboscopewhich alternates light and dark upon a photodiode. Also, the motorcontroller 113 can be used to detect how fast the gearmotor drive 103 isrotating (e.g., by a tachometer attached to the gearmotor driver 103 orby detecting back EMF).

As material travels from the product storage supply 102 to outputopening 107, it passes over the weigh idlers 105 which ride below thetop half of the belt 114. The weigh idlers 105 are unpowered (e.g.,idle) pulleys that allow the belt 114 to pass freely over them andprovide support for the belt 114 and material transported on it. Theweigh idlers 105 are coupled to the weigh bridge 117, which is in turncoupled to the weighing system. Thus, the weight of the material on thebelt 114, passing over the weigh idlers 105, is detected by the weightsensor 106. The weight sensor 106 is discussed in more detail herein.

In this implementation, one side of the rear pulley 116 is mounted on atake up bearing 108. The other side of the rear pulley (i.e., the farside in this perspective) is fixed in place, but is slidable (e.g.,adjustable) to maintain the desired tension on the belt 114 (see FIG.3B). Other implementations may utilize take up bearings 108 on bothsides of the rear pulley 116. To adjust the side of the rear pulley 116mounted on the take up bearing 108, a driveshaft 110 is coupled to thetake up bearing 108. The driveshaft 110 is in turn coupled to a trackinggearmotor 109. The tracking gearmotor 109 causes the driveshaft 110 torotate, thereby causing the rear pulley 116 mounted on the take upbearing 104 to translate horizontally either toward the front (e.g.,toward the output opening 107) or toward the rear of the belt 114 (e.g.,toward tracking gearmotor 109). The direction of translation (if any) isbased upon what is needed to address mis-tracking (if any) of belt 114.

The operation of the system is managed by one or more controllers. Thecontrollers can be implemented in various ways, including, e.g., a PCprogrammed with appropriate software, a PLC, and/or aproprietary/customized interface utilizing EEPROMs or other programmablememory. In this illustration, the controllers are shown as threeseparate entities 111, 112 and 113, but they may be implemented by asingle piece of hardware or software, or in as many separate componentsas is expedient for the particular application.

The weigh feeder controller 112 receives signals from the weight sensor106 which indicates the weight of the material on the belt 114 passingover weigh idlers 105. In a weigh feeder, this signal is received by theweigh feeder's controller for feed rate calculation purposes. In turn,the weigh feeder's controller outputs a command to the feeder's variablespeed controller 113 to control the speed of the gearmotor 103 asrequired to ensure the selected material flow rate is acheived.Alternatively, the variable speed controller can control, e.g., themotor in a screw conveyor in the product storage supply 102. In otherwords, the weight signal 106 can be used to control the speed of thebelt 114 or the speed at which material is supplied to the belt 114 inrelation to a feed rate selection. In some applications, the variablespeed controller 113 operates in a closed-loop configuration, e.g., ituses a feedback loop that detects the speed of the gearmotor 103 and/orbelt 114 and adjusts accordingly. The feedback loop may utilize a signalfrom speed sensor 104, and may receive that signal from the weigh feedercontroller 112. In still other implementations, the system 100 can beused as a weigh belt weigher where the speed of the gearmotor 103 ismaintained constant, with its speed designed to adequately handle therequired flow rate. In such an implementation, the variable speedcontroller 113 is configured to provide a constant speed. This can alsobe implemented by replacing variable speed controller 113 and gearmotor103 with a purpose-built constant speed drive. Controller 113 can thustake many forms, including a dedicated controller (e.g., the Acrison,Inc. 060 or 040 motor controllers).

The weigh feeder 100 includes one or more sensors (discussed below) thatdetect whether the belt 114 is mis-tracking in one direction or another.Signals from these sensors are passed to the weigh feeder controller112. The speed sensor 104 passes a signal to the weigh feeder controller112 indicative of the belt speed. The tracking controller 111 receivesthe signals from the mis-tracking sensors and the speed sensor 104 fromthe weigh feeder controller 112. Based upon whether the mis-trackingsensors have been triggered, the tracking sensor causes the trackinggearmotor to rotate in a direction that will address the mis-tracking.In some implementations, multiple mis-tracking sensors are used toenable the tracking controller 111 to determine what type of rotation ofthe tracking gearmotor 109 is needed to address the mis-tracking. Insome implementations, the one or more mis-tracking sensors detect theextent or degree of mis-tracking. The tracking controller 111 can alsoreceive a signal indicative of the belt speed. This is done in someimplementations so that the speed and/or frequency at which the take upbearing 108 is adjusted varies based on the belt speed. For example, atfaster belt speeds, the take up bearing 108 can be adjusted at a slowerpace than when the belt 114 is at a low speed.

FIG. 2 is a more detailed diagram of an implementation of a weigh beltweigher/feeder. As before, a chassis 101 is provided to maintain theoperational relationships of the mechanical elements. The desired supplyhopper or conveyor is coupled to the input 201, which directs materialonto the belt 114. The belt 114 is mounted between the front pulley 115and rear pulley 116. The rear pulley 116 is mounted on a take up bearing108. In this implementation, the take up bearing 108 is mounted on takeup bearing rails 204. The take up bearing 108 and bearing rails 204 arecomponents of the bearing assembly 208 (but other components may also beincluded). The take up bearing 108 translates along the rails 204 (e.g.,in a direction either away from or toward product output opening 107).The rotation of driveshaft 110 (coupled to the bearing assembly 208 bythe drive socket 207) causes the take up bearing 108 to translate oneway or another along the rails 204. The driveshaft 10 is coupled totracking gear assembly 203, which is coupled to tracking motor 202. Thetracking gear assembly 203 can include, e.g., a reduction gear toincrease torque or can be direct drive. The tracking motor 202 can be ACor DC, induction or synchronous, commutated or brushless, and/or couldtake the form of a stepper motor. The tracking gear assembly 203 andtracking motor 202 are mounted to the chassis 101 by mounting means 205,which can take the form of welding, bolt(s), screws, or the like.

As the driveshaft 110 rotates (e.g., upon rotation of the tracking motor202), it causes the take up bearing 108 to translate along the rails204. This causes the angle defined by the longitudinal axis of the rearpulley 11 6 to vary. In most implementations, the variance of the angleof the rear pulley does not affect rotational performance because thebearings employed are self-aligning.

FIG. 3A is a diagram of an implementation of a mis-tracking adjustmentmechanism, and more particularly, illustrates in detail the areaindicated generally by region 206 in FIG. 2. Visible in this view arebearing assembly brackets 301. The brackets 301 attach the bearingassembly 208 to the chassis 101. Secure attachment is beneficial toensure that the take up bearing 108 can translate smoothly with respectto chassis 101.

The take up bearing 108 and other portions of the take up bearingassembly 208 are usually made from metals such as bronze, iron, orsteel. Other materials are useable depending upon the implementation.

The pulley rotates about a bearing 302. Bearing 302 is, in mostimplementations, a self-aligning bearing. Depending on the application,self-aligning bearings are generally constructed with the inner ring andball assembly contained within an outer ring that has a sphericalraceway. This construction allows the bearing to tolerate angularmisalignment resulting from the deflection that may arise as the take upbearing 108 slides along the rails 204.

FIG. 3B is an alternate view of a weigh belt weigher/feeder system. Thisillustration is of the fixed side of a weigh belt weigher/feeder systemimplementation that adjusts one side of the rear pulley 11 6. This viewis from the perspective of FIG. 2, but with the chassis 101 rotated 180degrees about the vertical axis. As compared to, e.g., FIG. 2, somefeatures have been omitted for clarity.

Similar to the side of the rear pulley 116 that is adjustable, the rearpulley is mounted on a bearing 308. Like various other bearingsthroughout the system, bearing 308 is a self-aligning type. The bearing308 can translate along rails 311 in response to rotation of theadjustment shaft 312. In some implementations, the adjustment shaft 312is set for optimal belt tension and/or alignment during initial set up,and the bearing 308 remains in a fixed position relative to the rails311 unless the adjustment shaft 312 is re-adjusted. The rails aremounted to chassis 101 via brackets 310, which maintains the rails 311and bearing in a secure relationship relative to the chassis 101.

The front pulley 115 is also mounted on a bearing 305. The bearing 305is self-aligning, and is coupled to a plate 307 that is fixedly attachedto the chassis 101. In some implementations, the front pulley 115 is notadjustable. In this implementation, a tachometer 306 is coupled to thebearing 305 to sense the rotational speed of the front pulley 115. Insome implementations, a tachometer is placed on the pulley that is notdriven since it is not as susceptible to slippage due to the drivetorque. This may increase the accuracy of belt speed detection.

FIGS. 4A and 4B depict an implementation of a substantiallyfrictionless, lever type weighing system (which may be an aspect of theweight belt weigher/feeder system 100) that utilizes flexural pivots(flexures) for all pivotal connections associated with the variousmembers of the lever mechanism. Two primary flexures 401 and 402 connecteach of the two primary weigh beams 403 and 404 to the main framework ofthe lever weighing system (e.g., a portion of chassis 101). The twoweigh beams 403 and 404 are joined together with a linkage assemblyequipped with two flexures 405. Four additional flexures 408 and 411,located at each of the four ends of weigh beams 403 and 404, support andconnect weighbridge assembly 117 to the rest of lever weighing system.The design of these flexures provides rigidity in both the horizontaland vertical planes, greatly enhancing the ability of the weighingsystem to maintain its calibration and accuracy. Weight sensor 106,attached to the lever mechanism, measures vertical movement (ordisplacement) of the lever mechanism as weight is applied or removedfrom the weighbridge 117 (e.g., as the belt 114, and material thereon,passes over the weighbridge 117). The lever weighing system includes adashpot 407 to dampen (e.g., eliminate) any undesirable instability(e.g., bouncing) of the lever mechanism. In this implementation, themajority of the weighing system is mounted above the weigh belt 114,away from the material feed zone.

As the belt 114 passes over the weigh idlers 105 of weighbridge 117, theweight of material on the belt 114 causes the lever weighing system tomove in a very precise and linear relation to that weight (the weight ofthe belt 114 itself is, in some implementations, “tared-off” so thatonly the weight of the material on the belt is weighed). This movement(or displacement) of the lever weighing system is sensed by the DigitalWeight Resolver 406, which is a displacement transducer, and converts(substantially instantaneously) the displacement into a binary coded,serially transmitted data stream indicative of weight, having a discreteresolution of 20 bits (i.e., 1 part in 1,048,576).

FIG. 4A depicts a first case of belt mis-tracking. Here, the belt 114 istracking too far to the left, and triggering first mis-track sensor 409.In other implementations, mis-track sensors can disposed to sensemis-tracking by detecting the movement of the upper half of the beltrather than the lower half (e.g., sensors 412 and 413). In this case,because the mis-track sensor 409 has been triggered, the control systemwill adjust the take up bearing such that the belt will move away frommis-track sensor 409 while the device is in use.

Mis-track sensor 409 can take many forms, including, for example, acontact switch (e.g., one that closes or opens one or more circuits uponthe belt contacting the switch), a transmitter/receiver (e.g., one inwhich a signal passes from the transmitter to the receiver, and istriggered when mis-tracking interrupts the signal's passage), or aninductance proximity sensor. Myriad other arrangements are possible,with contact-type switches (e.g., those that require the belt toactually contact the switch) often used in most implementations.Regardless of the particular type of sensor 409, it is beneficial insome implementations that the sensor 409 be capable of detecting morethan one stage of mis-tracking. For example, one inch of mis-trackingmay trigger detection of stage 1 mis-tracking, two inches ofmis-tracking may trigger detection of stage 2 mis-tracking, three inchesof mis-tracking may trigger detection of stage 3 mis-tracking, and soon. A multi-stage switch is one manner of implementing such a sensor. Amulti-stage switch, as may be implemented in a mis-tracking system,generally comprises a member that is displaced relative to the switchhousing when contacted by an edge of the belt. The multi-stage switch iscapable of discerning the degree to which the member is displacedrelative to the switch housing, and thus can detect the degree to whichthe belt is mis-tracking. Another manner is using an array oftransmitter/receivers. Yet another manner is associating differentvoltage levels from an inductance proximity sensor with different stagesof mis-tracking.

FIG. 4B depicts a second case of belt mis-tracking. Here, the belt 114is tracking too far to the right, and triggering the second mis-tracksensor 410. In other implementations, mis-track sensors can disposed tosense mis-tracking by detecting the movement of the upper half of thebelt rather than the lower half (e.g., sensors 412 and 413). In thiscase, because the mis-track sensor 410 has been triggered, the controlsystem will adjust the take up bearing such that the belt will move awayfrom mis-track sensor 410.

FIG. 5 is a schematic of an implementation of an automatic beltmis-tracking correction system. The controller 505 is responsible for,among other things, receiving data from various sensors, and based onthat data, controlling the behavior of the system. The controller cantake many forms, and can be embodied in a general purpose computerprogrammed with appropriate software, a PLC (e.g., one that isprogrammable using the IEC 61131-3 standard graphical and/or textualprogramming language(s)), or various other programmable electronics(e.g., EEPROMs). Controller 505 may include all or some of the elements111, 112, and 113 of FIG. 1. Sensor 1 (501) and sensor 2 (503) send datato the controller 505 indicative of whether, and to what extent, a beltis mis-tracking in one direction or another. For example, sensor 1 (501)may be triggered when a belt mis-tracks to the left, whereas sensor 2(503) may be triggered when a belt mis-tracks to the right. Moreover,the sensors 501 and 503 can be capable (in at least someimplementations) of detecting more than one degree of mis-tracking. Inother words, the sensors 501 and 503 can be capable of determining notonly whether the belt is mis-tracking, but also how much it ismis-tracking. Thus, some implementations of the system can correct notjust dangerous amounts of mis-tracking, but can also be used to keep thebelt (e.g., 114) centered.

Belt speed sensor 502 sends data to the controller 505 indicative of howfast the belt is traveling. Belt speed sensor 502 can take the form of,e.g., a tachometer. Sensors 501, 502 and 503 may be wired directly tothe controller 505 or they may use a wireless or otherwise networkedconnection. In some implementations, the controller 505 is in a locationremote from other elements of the system. Given that, it should beunderstood that the lines indicating communication between varioussystem elements can include wired or wireless connections, networkedconnections, internet connections and the like.

In some implementations, it is beneficial that the controller 505monitor data from sensors 501, 502 and 503 (e.g., intermittently orcontinuously). The manner in which controller 505 controls the system(informed by data from sensors 501, 502 and 503) is dependent onparameters 504. Parameters 504 can be stored in an electronic data storethat is coupled to controller 505, and may be the part of the samehardware that makes up controller 505. In cases where the controller 505is managed remotely [e.g., via an internet, cellular, public switchedtelephone network (“PSTN”), LAN, WAN or wireless connection], theparameters 504 may be stored remotely or locally. The parameters 504 caninclude data such as: mis-tracking thresholds for one or more stages ofmis-tracking, acceptable belt speed ranges, when to stop the belt due tomis-tracking, when to sound an alarm due to mis-tracking, the extent thespeed of belt-tracking adjustments should be dependent upon belt speed,etc.

In some implementations, the controller 505 is coupled to a log 506. Thelog records events such as when (and to what extent) mis-trackingoccurred. This can allow, for example, an operator to correlate certainprocess events with greater incidence of mis-tracking. This may allowoperators to optimize certain process steps to prevent, e.g.,mis-tracking that requires operator intervention. Moreover, the log 506can be used to inform the controller 505 so that during instances when(historically speaking) mis-tracking is likely, the controller can takesteps to actively prevent mis-tracking. For example, the controller 505can take read data from sensors 501, 502 and/or 503 more frequently orcause the tracking motor 512 to adjust mis-tracking more aggressively(e.g., more quickly). The configuration relating to these features canbe stored in parameters store 504.

When the controller 505 detects that a mis-tracking condition existsbased on signals from sensors 501 and/or 503, it takes steps to addressit. Depending on one or more signals from the sensors 501 and/or 503,the controller 505 determines whether the belt is mis-tracking in afirst (e.g., left) or second (e.g., right) direction. The controller 505also determines, based on a signal from belt speed sensor 502, how fastthe belt is moving. The controller 505 sends a signal to the trackingmotor driver 509 to cause the tracking motor 512 to adjust a rear pulleyin a direction that addresses the mis-tracking. The tracking motordriver 509 can be, for example, an AC, DC, or stepper motor driver(depending upon the configuration of the tracking motor 512). Thetracking motor driver 509 can also take the form of a variable speedcontroller such as the Acrison, Inc. 060 or 040 DC motor controller orit may fix the speed of the tracking motor driver 509 at a constantspeed. In some implementations, the tracking motor 512 is coupled to adriveshaft that is coupled to a take up bearing, on which a rear pulleyis mounted. Rotation of the driveshaft causes the take up bearing tomove in either a first or second direction, thereby adjusting the rearpulley. The adjustment can occur at a rate that varies with the beltspeed detected by belt speed sensor 502. The configuration relating tothese features can be stored in parameters store 504.

In cases where the controller 505 determines that a certain level ofmis-tracking has been exceeded (e.g., stage 2 mis-tracking), it cancause an alarm 507 to be triggered. The alarm 507 can be local to thesystem, or can be remote. Alternatively, the alarm 507 can cause certainpersonnel to be alerted (e.g., via an e-mail, a pager call, a phonecall, a text message, etc.). Also, the controller 505 can be programmedto stop the gearmotor 511 (which rotates the belt) when a certain levelof mis-tracking is exceeded. The controller 505 interfaces with thegearmotor driver 510 which can be, for example, a DC, AC or steppermotor driver (depending on the configuration of gearmotor 511). Thetracking motor driver 509 can also take the form of an “off-the-shelf”variable speed controller such as the Acrison, Inc. 060 or 040 DC motorcontroller. The configuration relating to these features can be storedin the parameters store 504.

FIG. 6 is a flow chart illustrating an implementation of a method forautomatic belt mis-tracking correction. The first step involvesreceiving sensor signals (602). The sensor signals can be from one ormore sensors disposed proximate to the belt, in a position wheremis-tracking can detected by the sensors. In some implementations, abeneficial position is to place them on the weighbridge or lever systemof the weight sensor. This enables detection of mis-tracking in asensitive area of the system, and is also an area in which measurementsare taken. Next, based on the received signals, it is determined if afirst mis-tracking threshold has been surpassed (603). The magnitude ofthat threshold can be obtained from the threshold data store 601, whichinforms steps 603 and 606.

If the first mis-tracking threshold has not been surpassed (604), it ispresumed that the system is operating normally. This method continues,e.g., in a loop, to receive sensor signals (602) and test them (603).

If the first mis-tracking threshold has been surpassed (605), the nextstep is to determine whether a higher order mis-tracking threshold hasbeen surpassed. Higher order mis-tracking thresholds correspond togreater amounts of mis-tracking. Certain amounts of mis-tracking can beaddressed by automatic adjustment, whereas some greater amounts are notas amenable. For example, in a multi-stage system, stages 1, 2 and 3 caninclude belt adjustment (e.g., adjusting the rear pulley) while the beltis moving, whereas stage 4 can involve stopping the belt entirely (e.g.,Stage 1—adjusting the belt; Stage 2—slowing the belt, then adjusting thebelt, Stage 3—slowing the belt, then adjusting it aggressively; Stage4—stopping the belt, sounding an alarm and shutting off the materialfeed). In other implementations, the stages are not discrete, but ratherare a continuum from zero mis-tracking up to (and beyond) catastrophicmis-tracking. In this implementation of the method, first (603) andsecond (606) stages are illustrated.

If the second mis-tracking threshold is surpassed (607), the methodsounds an alarm and stops the belt (608). In this implementation, thesecond mis-tracking threshold represents a level of mis-tracking that isnot corrected automatically, but instead requires intervention frompersonnel.

If the second mis-tracking threshold is not surpassed (609), the methoddetermines what type of adjustment is needed to address the mis-tracking(610). This step is, generally speaking, related to the type andarrangement of sensors used to detect mis-tracking. For example, if thesystem is utilizing one or more switches on either side of the belt, themethod determines the direction of needed adjustment based on whichsensor is triggered. For example, if a sensor on the right side of thebelt is triggered, step 610 determines that the belt has moved too farto the right, and that it must adjust (611) to move the belt to theleft. In some implementations, the adjustment (611) is accomplished byadjusting a take up bearing coupled to a rear pulley. In anotherimplementation, the mis-tracking sensors may include a linear array oftransmitters and receivers and circuitry and/or logic that detects whenthe signal from one transmitter does not reach its respective receiver.In such an implementation, step 610 would determine on which side of thebelt are more receivers not receiving the transmitted signal. That sidewould represent the direction in which the belt is mis-tracking. Themethod would then adjust (611) accordingly.

The pulley adjustment 611 is informed by receiving a signalrepresentative of the belt speed 612.

In one implementation of tracking adjustment, the speed at which thetracking motor operates (to adjust for a mis-tracking condition) isdetermined by the speed of the belt. In this implementation, thetracking motor is a variable speed motor, slaved to the speed of thegearmotor drive powering the belt (e.g., in a fixed ratio, factory set,based on established parameters that optimize tracking adjustment). Inthis implementation, the faster the belt is moving, the faster the speedof the tracking motor.

In another implementation, which may be implemented at lower cost, thespeed of the tracking motor (to adjust for a mis-tracking condition) isfixed (e.g., a constant speed gearmotor drive). The variable which isbased on the speed of the belt is the length of the time the trackingmotor operates, and the “dwell” time between corrections (this can beanalogized to the “duty cycle” of the motor). As the belt slows, thedwell time increases (i.e., the duty cycle is decreased) when adjustingfor mis-tracking.

Various features of the system may be implemented in hardware, software,or a combination of hardware and software. For example, some features ofthe system may be implemented in computer programs executing onprogrammable computers. Each program may be implemented in a high levelprocedural or object-oriented programming language to communicate with acomputer system or other machine. Furthermore, each such computerprogram may be stored on a storage medium such as read-only-memory (ROM)readable by a general or special purpose programmable computer orprocessor, for configuring and operating the computer to perform thefunctions described above.

A number of implementations of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, the automatic belt tracking system can be employed with weighbelt weighers, weigh belt feeders, or any other apparatus that conveysmaterial utilizing a belt. Moreover, various sensors, controllers, andmechanisms can be employed in carrying out the system. Accordingly,other embodiments are within the scope of the following claims.

1. A belt mis-tracking adjustment apparatus comprising: a first pulleyhaving two ends and an axis of rotation, at least one of the ends iscoupled to a slidable bearing that enables translation of the end in adirection substantially perpendicular to the axis of rotation of thefirst pulley; a motor having a rotatable output shaft coupled to theslidable bearing, wherein the rotation of the output shaft in a firstdirection causes the slidable bearing to translate in a first directionand rotation of the output shaft in a second direction causes theslidable bearing to translate in a second direction; a second pulleyarranged at a distance from the first pulley; a belt coupled to thepulleys, the belt having two edges parallel to its direction of travel;a first contact sensor disposed adjacent to a first edge of the belt; acontroller coupled to the sensor and the motor, wherein if the firstedge of the belt contacts the first contact sensor, the controller isadapted to cause the motor to rotate the output shaft.
 2. The apparatusof claim 1 comprising: a second contact sensor disposed adjacent to asecond edge of the belt; wherein if the first edge of the belt contactsthe first contact sensor, the controller causes the motor to rotate theoutput shaft in the first direction, and if the second edge of the beltcontacts the second contact sensor, the controller is adapted to causethe motor to rotate the output shaft in the second direction.
 3. Theapparatus of claim 1 comprising a second motor coupled to the firstpulley for causing the first pulley to rotate about its axis ofrotation.
 4. The apparatus of claim 1 comprising a speed sensor coupledto the first pulley for generating a first speed signal.
 5. Theapparatus of claim 1 comprising a speed sensor coupled to the secondpulley for generating a second speed signal.
 6. The apparatus of claim 4wherein the controller adjusts the rate of rotation of the rotatableshaft based on the first speed signal.
 7. The apparatus of claim 5wherein the controller adjusts the rate of rotation of the rotatableshaft based on the second speed signal.
 8. The apparatus of claim 2wherein: the first contact sensor and the second contact sensor compriserespective contact members which are constructed to be depressed uponcontact with a respective edge of the belt; and the first contact sensorand second contact sensor are each operable to generate a signalrepresentative of the degree to which each respective contact member isdepressed.
 9. The apparatus of claim 8 wherein the controller comprises:stage identification logic for assigning a stage to a mis-tracking statedepending upon the signal representative of the degree to which acontact member is depressed based on predetermined stage parameters, thepredetermined stage parameters including a first stage representative ofa first degree of mis-tracking and a second stage representative of asecond degree of mis-tracking, the second degree being larger than thefirst degree; stage correction logic capable of causing the rotation ofthe rotatable shaft at a first rate in cases of a first stage andcapable of causing the rotation of the rotatable shaft at a second ratein cases of a second stage.
 10. A belt conveyor system comprising: afirst pulley having two ends; a second pulley spaced a distance from thefirst pulley; a belt mounted on the first and second pulleys, the belthaving two edges parallel to its direction of travel, the belt formingan endless loop around the first and second pulleys; a drive motorcoupled to the second pulley, wherein rotation of the drive motor causesrotation of the second pulley, and wherein rotation of the second pulleycauses the belt to travel such that at least one substantially linearportion of the belt travels in a direction substantially perpendicularto the axis of rotation of the second pulley; a slidable bearing coupledto at least of one of the ends of the first pulley which allowstranslation of the end in a direction substantially parallel to thetravel of at least one linear portion of the belt; a tracking motorhaving an output shaft coupled to the slidable bearing, wherein therotation of the output shaft in a first direction will cause theslidable bearing to translate in a first direction and rotation of theoutput shaft in a second direction will cause the slidable bearing totranslate in a second direction; a contact sensor disposed adjacent to afirst edge of the belt; a controller coupled to the sensor and thetracking motor adapted to cause the motor to rotate the output shaft ifthe first edge of the belt contacts the first contact sensor.
 11. Thesystem of claim 10 comprising: a second contact sensor disposed adjacentto a second edge of the belt; wherein the controller is adapted to:cause the motor to rotate the output shaft in the first direction if thefirst edge of the belt contacts the first contact sensor, and cause themotor to rotate the output shaft in the second direction if the secondedge of the belt contacts the second contact sensor.
 12. The system ofclaim 10 comprising a speed sensor coupled to the first pulley or secondpulley for generating a first speed signal.
 13. The system of claim 12wherein the controller adjusts the rate of rotation of the output shaftbased on the first speed signal.
 14. The system of claim 11 wherein: thefirst contact sensor and the second contact sensor comprise respectivecontact members which are adapted to be depressed upon contact with arespective edge of the belt; and the first contact sensor and secondcontact sensor are operable to generate a signal representative of thedegree to which each respective contact member is depressed.
 15. Thesystem of claim 14 wherein the controller comprises: stageidentification logic for assigning a stage to a mis-tracking statedepending upon the signal representative of the degree to which acontact member is depressed based on predetermined stage parameters, thepredetermined stage parameters including a first stage representative ofa first degree of mis-tracking and a second stage representative of asecond degree of mis-tracking, the second degree larger than the firstdegree; stage correction logic capable of causing the rotation of theoutput shaft at a first rate in cases of a first stage and capable ofcausing the rotation of the output shaft at a second rate in cases of asecond stage.
 16. The system of claim 15 wherein: the predeterminedstage parameters include a third stage representative of a third degreeof mis-tracking, the third degree larger than the second degree; and thestage correction logic slows the rotation of the drive motor in cases ofthe third degree of mis-tracking.
 17. The system of claim 10 comprising:an input port for receiving material to be conveyed on the belt; and aweigh sensor disposed adjacent a linear portion of the belt forgenerating a signal representative of the weight of the material on thebelt.
 18. A method for automatically addressing belt mis-tracking in abelt conveyor having a belt mounted on first and second pulleys,comprising: receiving a signal indicative of mis-tracking when an edgeof the belt has contacted a contact sensor; detecting the speed of thebelt; and automatically adjusting an end of second pulley upon detectionof mistracking, the rate of adjustment being related to the speed of thebelt.
 19. The method of claim 18 wherein the contact sensor comprisesfirst and second multi-stage switches, the method comprising: receivinga signal from the first multi-stage switch indicative of the degree towhich a belt is mis-tracking in a first direction; and receiving asignal from the second multi-stage switch indicative of the degree towhich a belt is mis-tracking in a second direction.
 20. The method ofclaim 19 comprising: automatically adjusting the end of the secondpulley so that the belt moves in the second direction if the belt ismistracking in the first direction; automatically adjusting the end ofthe second pulley so that the belt moves in the first direction if thebelt is mistracking in the second direction.
 21. The method of claim 19comprising: defining a first degree of mis-tracking; defining a seconddegree of mis-tracking, the second degree being greater than the firstdegree; in instances of a first degree of mis-tracking, adjusting an endof the second pulley at a first speed; and in instances of a seconddegree of mis-tracking, adjusting an end of the second pulley at asecond speed, the second speed being greater than the first speed. 22.The method of claim 21 comprising: defining a third degree ofmis-tracking, the third degree being greater than the second degree; andin instances of a third degree of mistracking, generating a notificationsignal.
 23. The method of claim 22 wherein generating a notificationsignal comprises at least one of sounding an alarm, sending an email,and initiating telephonic communication.
 24. An article comprising amachine-readable medium that stores machine-executable instructions forcausing a machine to: receive a signal from a first multi-stage switchindicative of the degree to which a belt is mis-tracking in a firstdirection; receive a signal from a second multi-stage switch indicativeof the degree to which the belt is mis-tracking in a second direction;detect the speed of the belt; adjust the end of the second pulley sothat the belt moves in the second direction if the belt is mistrackingin the first direction, with the rate of adjustment being related to thespeed of the belt; and adjust the end of the second pulley so that thebelt moves in the first direction if the belt is mistracking in thesecond direction, with the rate of adjustment being related to the speedof the belt.